Development of solid matrix priming to enhance loblolly pine (Pinus taeda) seed germination and analysis of its physiological mechanisms

Scope and method of study. The objectives of this study were to determine the physiological and genetic mechanisms responsible for the invigoration of loblolly pine seeds subjected to controlled drying through solid matrix priming (SMP) after stratification and develop advanced seed treatments for improving nursery production of seedlings. Changes in water potential, protein content and profiles, number and size of protein bodies were investigated during SMP and subsequent germination. Effects of RNA/protein synthesis inhibitors and protease inhibitors on the above indices were compared. Induction of thiol protease (TP) gene expression by SMP and effects of the inhibitors on the induction were analyzed at transcription and translation levels. Activity of TP influenced by SMP and by the inhibitors were measured.; Findings and conclusions. Experimental results showed: (1) TP gene transcript accumulation was upregulated by SMP and (2) the upregulation was further reflected at TP gene translation and enzyme activity levels. The correlations among water potential, protein profiles, protein bodies, TP gene expression, TP activity and effects of inhibitors on the above indices suggest the increased TP is involved in the mobilization of reserve proteins during SMP. The results indicate that the invigoration is due to a change in the sequence of events in the germinating seed where storage protein mobilization which normally commences after germination is stimulated before radicle emergence. The mobilization of storage proteins may provide: (1) substances for osmotic adjustment leading to increased capacity of the embryo to grow and (2) the components for synthesis of new proteins for the growing plant. The SMP treatment for seed lots from 5 open-pollinated families that gave the greatest rapidity and synchrony of germination was 6 d of priming, 30 to 35% matrix moisture content and seed to matrix ratio 1:1 to 1:4. SMP could partly replace stratification to break seed dormancy and one week post-SMP storage showed no negative effects on the improvement of germination by SMP.